This invention relates to the manufacture of metals and, notably, steel. It concerns, in particular, the pneumatic refining of a cast iron bath contained in a crucible with oxygen blown at the top.
It is known that a refining crucible with oxygen blown at the top is a metal vessel with a thick refractory lining. The vessel consists essentially of a cylindrical vertical part (called side wall), which is, on the one hand, closed at its lower end by a fixed circular bottom and, on the other, extended at its upper end by a truncated cone-shaped part forming the lip. A vertical nozzle enters through the latter for the blast of one or more refining oxygen jets in the direction of the surface of the metal bath contained in the crucible.
It is known that the metallurgical possibilities of the methods of refining cast iron by blowing oxygen at the top can be widened by injecting an agitating gas at the bottom of the crucible. That gas is usually chemically inert to impurities in the metal, like nitrogen, argon, etc., pure or mixed. But it is not out of the question to use a reagent gas, such as oxygen or CO.sub.2, whether pure or mixed with an inert gas and which, in addition to its agitating function, participates in the refining proper, by combining its action with that of the oxygen blown at the top.
It is known that the beneficial effects that can be expected from same are, notably, an easier handling of the blast and an improvement of the iron yield and of the quality of the steel, as well as a reduction of the consumption of deoxidizers and ferroalloys. One can also benefit from an increase in the quantity of coolant additions (scrap or ore), thanks to an increase in the rate of secondary combustion ##EQU1## when, as described, for example, in Luxembourg Patent Application No. 81,207, the process is used jointly with the maintenance of a well distributed oxygen atmosphere on the surface of the bath.